Schools paying for Grades

Today I heard in the students in (poorer) some areas are getting paid for grades. They are even paying them to do (standardized) tests. Even if these standardized tests are not required (to say, students can be exempt by their parents) and used to size-up how students are doing I must say my compulsion is to say students should not be paid for doing these tests. Do not get me wrong I fully understand that if students are not encourage by some means to write these tests then the chances are that only those that feel that they are going to do well will write as well as only those students from families that see education as realistic away to achieve (financial) success: this often means low-income families may see post-secondary as unreasonable because of the expenses. However, what about paying for achieving grades?

I can certainly see how this may motivate students. Is this practice fair: are students simply getting paid for the higher grades (e.g. As, Bs) or are they getting paid for achieving better grades each time (even if its by percentage increase)? Is there a specific amount that a student will earn if they get a C-, C, C+, B, A? Personally, I think paying them for achieving better each time is the best approach because it encourages them to improve themselves rather than just doing a minimum work. Granted some students are only would try to do the minimum and as such would not like this approach (or should I not even take part), but is the minimum behavior really is what we want to be encouraging: that is, do we what to encourage minimum as being counted as achieving more? More to the point of this fair ness issue is that there are some students regardless of how hard they try will only be able to achieve so high in terms of grades or for some reason it is unreasonable to expect them to be A or B student (such as those with cognitive or mental health problems).